Recently, communication traffics of radio signals in mobile terminal communication are tending to increase due to an increase in mobile terminals. In view of this, it is demanded to optically transmit radio signals in mobile terminal communication through an optical network that enables a large amount of data to be transmitted.
As for the optical network, a multi-carrier modulation system (such as, for example, a discrete multi-tone (DMT) modulation system) is used by which information signals are frequency-multiplexed to a plurality of subcarriers with different frequencies.
Japanese Laid-open Patent Publication No. 2004-112781 is an example of related art.
However, although it is demanded to optically transmit radio signals in mobile terminal communication through an optical network, it is difficult to efficiently transmit radio signals with a multi-carrier signal in which information signals are multiplexed.